Equine rotavirus is a potentially deadly virus that causes severe gastrointestinal symptoms in foals.

Rotavirus is one of the most common causes of diarrhea in foals less than 6 months of age. Animals younger than 2 months of age experience the most severe symptoms including dehydration and malabsorption of nutrients.

It is estimated that up to 50% of foals contract this virus. [1] Foals can become infected with rotavirus by ingesting fecal matter that carries viral particles. Adult horses can also contract and spread rotavirus, but they are generally asymptomatic.

This virus is highly contagious and can quickly become deadly in young foals. Careful bio-security measures must be taken to avoid infection and prevent the spread of this virus.

What is Equine Rotavirus?

Equine rotavirus is a double-stranded RNA, non-enveloped virus that is species-specific, meaning it cannot be transmitted to species other than horses.

Equine rotavirus attacks the villi of the small intestine, which are tiny finger-like projections that line the intestinal wall. Rotavirus causes cellular destruction, malabsorption, and severe diarrhea. [1]

The villi of the small intestine are responsible for absorbing and transporting nutrients from food that has been digested into the bloodstream.

Equine rotavirus attaches to the villi and damages the calcium ion transfer system, resulting in severe cell damage and death. When the villi are damaged and enterocytes are destroyed, the intestine’s ability to absorb nutrients is impaired. This results in diarrhea, intestinal swelling and immune activation. [2]

The inflamed small intestine is very painful and susceptible to ulceration. [11]

Rotavirus in Foals

Unlike adult horses, newborn foals are highly susceptible to equine rotavirus and can quickly become very ill.

Growing foals must be able to efficiently absorb and utilize the nutrients from their mother’s milk. If they contract rotavirus and cannot properly absorb nutrients from the intestinal tract, they can experience weight loss that may stunt their growth.

Foals under two months of age are most at risk of complications from equine rotavirus because:

  1. They are immunologically immature. Newborn foals do not have a fully developed immune system to fight off viruses entering their bodies. Foals receive antibodies to fight pathogens through colostrum produced by the mare, but they do not have the same immune defences as adult horses.
  2. Foals are incredibly curious and they explore the world with their mouths. Equine rotavirus is transmitted via the fecal-oral route. A foal needs only to lick a surface that has infected fecal matter particles to become ill with this virus. [2]

As the foal ages, the risk of severe infection from equine rotavirus decreases significantly. This virus is not considered a significant cause of diarrhea in foals over 6 months.

However, horses of all ages can carry equine rotavirus without displaying active symptoms. The majority of adult horses carry rotavirus antibodies, demonstrating previous infection. [2] Foals can even contract equine rotavirus from their mother, making isolation and prevention difficult. [3]

Mad About Horses
Join Dr. Chris Mortensen, PhD on an exciting adventure into the story of the horse and learn how we can make the world a better place for all equines.
Apple Podcasts Spotify Youtube
Mad Barn - Equine Nutrition Consultants | Mad Barn USA


The typical symptoms of equine rotavirus in foals depend on the age of the horse. Younger foals experience more severe symptoms than older foals. These symptoms are usually sudden and dramatic in onset.

Clinical signs of rotavirus in foals include:

Although these symptoms are usually mild in adult horses, young foals can quickly become critically ill. In some cases, foals infected with equine rotavirus will refuse to nurse, making dehydration worse.

Newborn foals receive all of their nutrition and water from their mother’s milk. If the foal refuses to nurse and cannot replace the nutrients and water lost in diarrhea, they can go into shock and succumb to the illness. [4]


Foals that become seriously ill with equine rotavirus can develop severe ulcers that are resistant to treatment. Because of inflammation of the small intestine and bowel, any milk the foal ingests moves quickly through the entire digestive tract.

This leaves the already sensitive mucosal tissues unprotected from stomach acid. Gastric juices can erode the unprotected lining of the stomach and small intestine, further inflaming the entire digestive tract.

The sick foal will exhibit signs of colic and be increasingly reluctant to nurse. [4]


Fortunately, quick intervention can save the foal from becoming severely ill. It is thought that almost 50% of foals become infected with equine rotavirus, but mortality is only 1%. Most foals recover well with proper veterinary attention.

However, equine rotavirus can cause significant weight loss and profound damage to the small intestine, leaving the foal weak and vulnerable. [4]


Treatment for equine rotavirus infection includes addressing the symptoms and supporting the health of the foal.

If you notice your foal has diarrhea and is not consistently nursing, contact your vet right away. Foals can become very sick in a short period of time. Early veterinary intervention is crucial for long-term success.

Immunoglobulin Test

Your veterinarian will first want to perform an IgG (immunoglobulin) test to determine if your foal has received adequate antibodies from the mare. [5]

When a foal is first born, they lack immune defences. Antibodies are transferred to them from the mare’s colostrum. If your foal does not receive the required antibodies from the mare they will be less able to defend against viruses and infections.

The antibody molecules that your foal absorbs through the mare’s colostrum are called immunoglobulins (Ig). Immunoglobulins are very large molecules that can only be absorbed from the gut within the first 24 hours of your foal’s life.

Your vet will take a blood sample from your foal and look for IgG levels over 800mg/dL. Levels of 400-799mg/dL indicate partial failure of passive transfer> Levels below 400mg/dL indicate a complete failure of passive transfer. [6]

Based on the results of the IgG test, your vet may suggest interventions to improve resistance to equine rotavirus and other infectious diseases.

If your foal is younger than 24 hours, your vet can provide supplementary colostrum that can be given orally to your foal. If your foal is older than 24 hours, your vet will need to give them an IV plasma infusion. [7]

Dietary Support

After supporting your foal’s immune system, your veterinarian will treat any clinical signs of equine rotavirus. At the home farm, your vet will provide:

  • Oral electrolytes (to be mixed with water and syringed into the foal’s mouth)
  • Probiotics to replenish the gut flora
  • Gastrointestinal protectants such as Kaopectate and Bio-sponge (a supplement to firm up the stool)
  • Appetite stimulants to encourage your foal to nurse

If your foal’s condition continues to decline and becomes dehydrated, your veterinarian may suggest hospitalization to administer IV fluids and/or nutrition through a nasogastric tube. [4]

To prevent the spread of infection to other foals, your vet will suggest complete isolation of the mare and foal. Because equine rotavirus can live on surfaces for up to 10 days after contact, any supplies or clothing leaving the foal’s stall must be completely disinfected with bleach or a rubbing alcohol solution. [4]


The key to preventing rotavirus infection is proper sanitization procedures and reducing cross-contamination.

Horses (especially foals) produce a large volume of fecal matter that can contaminate their environment. Viral particles in fecal matter can be picked up after even the most cursory interaction.

Experts suggest wearing disposable gloves while handling and treating foals under 6 months, even if the foal is not outwardly sick. Wearing disposable gloves ensures that foals and mares are never handled with unclean hands.

If you do not wear gloves, make sure to wash and sanitize your hands before and after handling the foal. You can also dip your boots in a bleach solution before entering the foal’s stall to avoid cross-contamination. [8]

Handling Foals with Rotavirus

If you have a foal with symptoms or a confirmed case of rotavirus, isolation of the mare and foal is absolutely necessary.

Infected foals produce watery diarrhea that can splatter and spread contagious droplets across long distances. Isolation is necessary to keep other foals and horses in the stable safe. [8]

When handling a foal with rotavirus, sanitize and change your clothes before touching any other surfaces.

Washable overalls are recommended; put a clean pair of overalls on top of your clothes before entering the stall and then take them off and put them in a garbage bag to be thoroughly washed after you are done.

Any syringes used to administer medication to the foal must be discarded. [8]

Stable Management

Wash your hands with anti-microbial soap and use a bleach dip on your boots to ensure you do not transport contaminated fecal matter into or out of the stall.

This will keep the compromised foal from catching any other illness and prevent the spread of equine rotavirus to other foals in the barn. [8]

Regularly scrub the entire stall with a disinfectant solution (i.e. bleach, Lysol®) throughout the foal’s recovery and before they return from the equine hospital. Remove all bedding and hay and thoroughly clean all water and feed buckets.

If possible, use a power washer to remove all debris and scrub all surfaces with a disinfecting solution.

Foals can become re-infected with equine rotavirus after treatment. Proper sanitization procedures will help to avoid recontamination from within their stall. [9]

Turnout Management

Avoid turning foals or adult horses out in a field that has housed a foal with rotavirus.

Although horses over 6 months old do not typically exhibit symptoms of rotavirus infection, they can spread the virus to younger foals and make them sick. [9]

If your foal with equine rotavirus has been turned out in a paddock with other foals, observe the other foals for possible illness.

Equine Rotavirus Vaccine

In 1977, an equine rotavirus vaccine was first developed and tested for use in pregnant mares. Similar to other pre-birth vaccines, the equine rotavirus vaccine is given to pregnant broodmares before giving birth to help protect the newborn foal.

The vaccine is meant to trigger the mare’s immune system to produce antibodies specific to equine rotavirus. The antibodies are then transferred to the mare’s colostrum, which is ingested by newborn foals.

The foal absorbs these antibodies, enabling their immune system to fight off equine rotavirus infection. This vaccine is administered at 7, 9, and 10 months of gestation. [10]

Unfortunately, foals may still contract equine rotavirus even if the mare received the rotavirus vaccine at the appropriate times during pregnancy. The vaccine has limited efficacy.

There are several variants of equine rotavirus, each of which has a slightly different structure. In order to be effective, the vaccine must match the variant that is contracted by the foal.

Despite the limited efficacy, most veterinarians will recommend the equine rotavirus vaccine if an outbreak has occurred at the farm in order to minimize the risk for the newborn foal. [10]

Supporting the Mare’s Immune System

Because newborn foals derive their immune system from their mare’s colostrum, supporting the immunity of the mare can help to protect foals from all kinds of diseases.

Mad Barn’s Optimum Digestive Health is a gut health supplement that also contains ingredients that support the immune system. Feeding this supplement to the breeding mare can help to kick-start the immune system of the young foal.

Immunity can be assessed by measuring the levels of immunoglobulins (IgA, IgG, IgM) present in the colostrum of mares. Immunoglobulins are proteins that contain antibodies that help to defend against infection from viruses and bacteria.

Supporting Foal's Immune System

In a research study, ingredients found in ODH were shown to significantly increase the level of immunoglobulins found in colostrum compared to a control. This results in a greater transfer of immunity to the growing foal.

Optimum Digestive Health

5 stars
4 stars
3 stars
2 stars
1 star

Learn More

  • Prebiotics, probiotics & enzymes
  • Support hindgut development
  • Combats harmful toxins in feed
  • Complete GI tract coverage


  • Equine rotavirus can live in the gastrointestinal tract of any horse, but will make foals under 6 months very ill.
  • The virus attacks villi in the small intestine, inhibiting nutrient and water absorption.
  • Infected foals exhibit watery diarrhea, lethargy, reluctance to nurse, a distended abdomen, and dehydration.
  • Prompt treatment with electrolytes, gastrointestinal protectants, appetite stimulants, and probiotics can save your foal.
  • Some foals will need hospitalization and intense treatment to recover.
  • Take care to sanitize and disinfect anything entering or leaving a foal’s stall, including your clothing and hands.
  • Consider vaccinating your mare for equine rotavirus before she gives birth.
  • With prompt treatment and diligent care, most foals recover from a bout of equine rotavirus. Foals may need dietary support to regain lost body condition.
  • Feeding an immune support supplement such as Optimum Digestive Health to your pregnant mare can promote the transfer of immunoglobulins to the newborn foal through colostrum.

If your foal is experiencing diarrhea from an infection with equine rotavirus, read our guide on how to feed a horse with diarrhea for suggestions on supporting recovery.

Is Your Horse's Diet Missing Anything?

Identify gaps in your horse's nutrition program to optimize their well-being.


  1. Collins, P. et al. Molecular Characterization of Equine Rotavirus in Ireland. Journal of Clin Microbiology. 2008.
  2. Bailey, K. et al. Equine rotaviruses—Current understanding and continuing challenges. Vet Microbiology. 2013.View Summary
  3. Magdesian, K. Neonatal Foal Diarrhea. Vet Clinics: Equine Prac. 2005. View Summary
  4. Connor, M. and Darlington, R. Rotavirus infection in foals. Am Journal of Vet Research. 1980.
  5. Davis, D. et al. Measurement of Serum IgG in Foals by Radial Immunodiffusion and Automated Turbidimetric Immunoassay. Journal of Vet Internal Med. 2008. View Summary
  6. Stoneham, S. et al. Failure of passive transfer of colostral immunity in the foal: incidence, and the effect of stud management and plasma transfusions. The Vet Record. 1991.View Summary
  7. Liepman, R. et al. Validation of IgG cut-off values and their association with survival in neonatal foals. Equine Vet J. 2015.
  8. Tzipori, S. and Walker, M. ISOLATION OF ROTAVIRUS FROM FOALS WITH DIARRHOEA. Immunology and Cell Bio. 1978. View Summary
  9. Dwyer, R. Environmental disinfection to control equine infectious diseases. Vet Clinics: Equine Practice. 2004. View Summary
  10. Powell, D. et al. Field study of the and efficacy an inactivated equine rotavirus. Journal of the Am Vet Med Assoc. 1997.
  11. Ramig, R. Pathogenesis of Intestinal and Systemic Rotavirus Infection. Journal of Virology. 2004.